[LLVMdev] radr://12777299, "potential pthread/eh bug exposed by libsanitizer"
Jack Howarth
howarth at bromo.med.uc.edu
Sat Dec 1 15:30:44 PST 2012
On Sat, Dec 01, 2012 at 05:42:15PM +0400, Kostya Serebryany wrote:
> +kremenek, ganna
>
> On Sat, Dec 1, 2012 at 4:33 AM, Jack Howarth <howarth at bromo.med.uc.edu>wrote:
>
> > On Fri, Nov 30, 2012 at 01:41:05PM +0400, Kostya Serebryany wrote:
> > > Just want to remind everyone that we plan to stop using mach_override in
> > > asanin favor of OSX's native function interposition.
> > > So, we probably don't want to spend too much effort fixing mach_override.
> > >
> > > --kcc
> >
> > Kostya,
> > Unless I am misunderstanding the code in
> > asan/asan_intercepted_functions.h,
> > using MAC_INTERPOSE_FUNCTIONS on FSF gcc will require the missing blocks
> > support
> > to be implemented. I did a quick and dirty attempt to build libasan using
> > libsanitizer/asan/dynamic/asan_interceptors_dynamic.cc imported from llvm
> > svn.
> > The bootstrap chokes on...
> >
>
> Alex is the expert in the OSX side of things, hopefully he can comment.
>
> But our situation wrt asan on OSX is as I see it:
> - mach_override does not work: we spent more time fighting with
> mach_override's stability than we spent on implementing all of asan for
> linux. And there are still bugs we don't know how to fix.
> - mach_override does not work: it is not supported on iOS and (may not
> be supported) on later versions of OSX
> So, there is no choice for us but to use the Apple-blessed mechanism.
>
> Do we want to support both?
> No, that's too expensive. And very likely once we move to function
> interposition, mach_override will rot very soon.
Kostya,
I've updated the proposed patch for switching from mach_override to
mac function interposition on http://gcc.gnu.org/bugzilla/attachment.cgi?id=28849
with the addition of the usage of -DMISSING_BLOCKS_SUPPORT and the appropriate
tests on that to avoid the missing blocks support on FSF gcc.
Jack
>
>
> >
> > /bin/sh ../libtool --tag=CXX --mode=compile
> > /sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/./gcc/xg++
> > -B/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/./gcc/ -nostdinc++
> > -nostdinc++
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include/x86_64-apple-darwin12.2.0
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/libsupc++
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/include/backward
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/testsuite/util
> > -L/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/src
> > -L/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/src/.libs
> > -B/sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/bin/
> > -B/sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/lib/ -isystem
> > /sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/include -isystem
> > /sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/sys-include -D_GNU_SOURCE
> > -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS
> > -D__STDC_LIMIT_MACROS -DASAN_HAS_EXCEPTIONS=1
> > -DASAN_FLEXIBLE_MAPPING_AND_OFFSET=0 -DASAN_NEEDS_SEGV=1
> > -DMAC_INTERPOSE_FUNCTIONS -I.
> > -I../../../../gcc-4.8-20121130/libsanitizer/asan -I
> > ../../../../gcc-4.8-20121130/libsanitizer/include -I
> > ../../../../gcc-4.8-20121130/libsanitizer -Wall -W -Wno-unused-parameter
> > -Wwrite-strings -pedantic -Wno-long-long -fPIC -fno-builtin
> > -fno-exceptions -fomit-frame-pointer -funwind-tables -fvisibility=hidden
> > -Wno-variadic-macros -Wno-c99-extensions -g -O2 -MT asan_interceptors.lo
> > -MD -MP -MF .deps/asan_interceptors.Tpo -c -o asan_interceptors.lo
> > ../../../../gcc-4.8-20121130/libsanitizer/asan/asan_interceptors.cc
> > libtool: compile:
> > /sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/./gcc/xg++
> > -B/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/./gcc/ -nostdinc++
> > -nostdinc++
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include/x86_64-apple-darwin12.2.0
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/libsupc++
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/include/backward
> > -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20121130/libstdc++-v3/testsuite/util
> > -L/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/src
> > -L/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/src/.libs
> > -B/sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/bin/
> > -B/sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/lib/ -isystem
> > /sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/include -isystem
> > /sw/lib/gcc4.8/x86_64-apple-darwin12.2.0/sys-include -D_GNU_SOURCE -D_DEBUG
> > -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
> > -DASAN_HAS_EXCEPTIONS=1 -DASAN_FLEXIBLE_MAPPING_AND_OFFSET=0
> > -DASAN_NEEDS_SEGV=1 -DMAC_INTERPOSE_FUNCTIONS -I.
> > -I../../../../gcc-4.8-20121130/libsanitizer/asan -I
> > ../../../../gcc-4.8-20121130/libsanitizer/include -I
> > ../../../../gcc-4.8-20121130/libsanitizer -Wall -W -Wno-unused-parameter
> > -Wwrite-strings -pedantic -Wno-long-long -fPIC -fno-builtin -fno-exceptions
> > -fomit-frame-pointer -funwind-tables -fvisibility=hidden
> > -Wno-variadic-macros -Wno-c99-extensions -g -O2 -MT asan_interceptors.lo
> > -MD -MP -MF .deps/asan_interceptors.Tpo -c
> > ../../../../gcc-4.8-20121130/libsanitizer/asan/asan_interceptors.cc
> > -fno-common -DPIC -o .libs/asan_interceptors.o
> > In file included from
> > ../../../../gcc-4.8-20121130/libsanitizer/asan/asan_interceptors.cc:15:0:
> > ../../../../gcc-4.8-20121130/libsanitizer/asan/asan_intercepted_functions.h:209:57:
> > error: expected ‘)’ before ‘^’ token
> > dispatch_queue_t dq, void (^work)(void));
> > ^
> > etc. So we may be stuck with mach_override until someone steps up to
> > implement the missing blocks support for darwin in FSF gcc.
> >
>
>
> --kcc
>
>
>
> > Jack
> >
> > >
> > > On Fri, Nov 30, 2012 at 4:46 AM, Alexander Potapenko <glider at google.com
> > >wrote:
> > >
> > > > Looks like this happens on x86_64 because the position of __cxa_throw
> > > > is too far from the allocated branch island (should be <2G). This can
> > > > be solved by allocating the branch islands somewhere near the text
> > > > segment (look for kIslandEnd in asan_mac.cc, this is currently
> > > > 0x7fffffdf0000) or by patching the function with a longer instruction
> > > > sequence that stores the jump target in a register and jumps to that
> > > > target (which is a bit more complex to implement).
> > > >
> > > > Once this problem is fixed, another one is going to arise. This is how
> > > > the first bytes of __cxa_throw look like:
> > > >
> > > > 0x0020c49ba5d916e0 <__cxa_throw+0>: lea 0xb4f01(%rip),%rax #
> > > > 0x20c49ba5e465e8 <_ZN10__cxxabiv120__unexpected_handlerE>
> > > > 0x0020c49ba5d916e7 <__cxa_throw+7>: push %rbx
> > > > 0x0020c49ba5d916e8 <__cxa_throw+8>: lea -0x20(%rdi),%rbx
> > > >
> > > > If we move the relative LEA instruction somewhere, we must fix the
> > > > constant in order to keep it pointing to the same address.
> > > > mach_override already does this for relative CALL and JMP
> > > > instructions, but not for LEA. This should be fairly simple to fix.
> > > >
> > > > Note that the 32-bit variant crashes on another invalid address:
> > > >
> > > > ASAN:SIGSEGV
> > > > =================================================================
> > > > ==89768== ERROR: AddressSanitizer: SEGV on unknown address 0xcccccccc
> > > > (pc 0x00061f8c sp 0xbffa8bd0 bp 0xbffa8cc8 T0)
> > > > AddressSanitizer can not provide additional info.
> > > > #0 0x61f8b
> > > > (/Users/glider/src/gcc-asan/inst/lib/i386/libstdc++.6.dylib+0x3f8b)
> > > > #1 0x91391724 (/usr/lib/system/libdyld.dylib+0x2724)
> > > > #2 0x0
> > > > Stats: 0M malloced (0M for red zones) by 3 calls
> > > > Stats: 0M realloced by 0 calls
> > > > Stats: 0M freed by 0 calls
> > > > Stats: 0M really freed by 0 calls
> > > > Stats: 1M (256 full pages) mmaped in 2 calls
> > > > mmaps by size class: 7:4095; 8:2047;
> > > > mallocs by size class: 7:1; 8:2;
> > > > frees by size class:
> > > > rfrees by size class:
> > > > Stats: malloc large: 0 small slow: 2
> > > > ==89768== ABORTING
> > > >
> > > > My guess is that this is caused by the following code being moved to a
> > > > branch island:
> > > >
> > > > Dump of assembler code for function __cxa_throw:
> > > > 0x00008f60 <__cxa_throw+0>: push %esi
> > > > 0x00008f61 <__cxa_throw+1>: push %ebx
> > > > 0x00008f62 <__cxa_throw+2>: call 0x7a60 <__x86.get_pc_thunk.bx>
> > > >
> > > > Perhaps this makes __x86.get_pc_thunk.bx return an incorrect value.
> > > >
> > > > Since libstdc++-v3 is built together with gcc, the two issues related
> > > > to instructions being moved to another place can be solved by padding
> > > > __cxa_throw() with five NOP instructions (enough to hold a JMP). I
> > > > believe this should be acceptable, because the performance penalty for
> > > > additional NOPs is negligible, and __cxa_throw() isn't a hot point.
> > > >
> > > > On Thu, Nov 29, 2012 at 1:01 PM, Nick Kledzik <kledzik at apple.com>
> > wrote:
> > > > > I debugged this a bit and it seems the mach_override patching of
> > > > __cxa_throw is bogus. The start of that function is patched to jump to
> > > > garbage.
> > > > >
> > > > > Breakpoint 1, 0x0000000100001c19 in main ()
> > > > > (gdb) display/i $pc
> > > > > 2: x/i $pc 0x100001c19 <main+318>: callq 0x100016386
> > > > <dyld_stub___cxa_throw>
> > > > > (gdb) si
> > > > > 0x0000000100016386 in dyld_stub___cxa_throw ()
> > > > > 2: x/i $pc 0x100016386 <dyld_stub___cxa_throw>: jmpq
> > > > *0xae1c(%rip) # 0x1000211a8
> > > > > (gdb)
> > > > > 0x0000000102244870 in __cxa_throw ()
> > > > > 2: x/i $pc 0x102244870 <__cxa_throw>: jmpq 0xffd27000
> > > > > (gdb) # the above its __cxa_throw in gcc's libstdc++.6.dylib. The
> > > > first instruction has been patch to jump to a garbage address.
> > > > >
> > > > > (gdb) x/8i 0x102244870-8
> > > > > 0x102244868
> > > >
> > <_ZL23__gxx_exception_cleanup19_Unwind_Reason_CodeP17_Unwind_Exception+56>:
> > > > std
> > > > > 0x102244869
> > > >
> > <_ZL23__gxx_exception_cleanup19_Unwind_Reason_CodeP17_Unwind_Exception+57>:
> > > > (bad)
> > > > > 0x10224486a
> > > >
> > <_ZL23__gxx_exception_cleanup19_Unwind_Reason_CodeP17_Unwind_Exception+58>:
> > > > decl (%rdi)
> > > > > 0x10224486c
> > > >
> > <_ZL23__gxx_exception_cleanup19_Unwind_Reason_CodeP17_Unwind_Exception+60>:
> > > > (bad)
> > > > > 0x10224486d
> > > >
> > <_ZL23__gxx_exception_cleanup19_Unwind_Reason_CodeP17_Unwind_Exception+61>:
> > > > add %r8b,(%rax)
> > > > > 0x102244870 <__cxa_throw>: jmpq 0xffd27000
> > > > > 0x102244875 <__cxa_throw+5>: or (%rax),%eax
> > > > > 0x102244877 <__cxa_throw+7>: push %rbx
> > > > > (gdb)
> > > > > (gdb) watch *0x102244870
> > > > > Hardware watchpoint 2: *4330899568
> > > > > (gdb) r
> > > > >
> > > > > Old value = -788165304
> > > > > New value = -1373139991
> > > > > 0x0000000100016203 in __asan_mach_override_ptr_custom ()
> > > > > (gdb) bt
> > > > > #0 0x0000000100016203 in __asan_mach_override_ptr_custom ()
> > > > > #1 0x0000000100015a9e in __interception::OverrideFunction ()
> > > > > #2 0x00007fff5fc13378 in ImageLoaderMachO::doModInitFunctions ()
> > > > > #3 0x00007fff5fc13762 in ImageLoaderMachO::doInitialization ()
> > > > > #4 0x00007fff5fc1006e in ImageLoader::recursiveInitialization ()
> > > > > #5 0x00007fff5fc0feba in ImageLoader::runInitializers ()
> > > > > #6 0x00007fff5fc01fc0 in dyld::initializeMainExecutable ()
> > > > > #7 0x00007fff5fc05b04 in dyld::_main ()
> > > > > #8 0x00007fff5fc01397 in dyldbootstrap::start ()
> > > > > #9 0x00007fff5fc0105e in _dyld_start ()
> > > > > (gdb) x/8i 0x102244870
> > > > > 0x102244870 <__cxa_throw>: jmpq 0xffd27000
> > > > > 0x102244875 <__cxa_throw+5>: or (%rax),%eax
> > > > > 0x102244877 <__cxa_throw+7>: push %rbx
> > > > > 0x102244878 <__cxa_throw+8>: lea -0x20(%rdi),%rbx
> > > > > 0x10224487c <__cxa_throw+12>: mov %rsi,-0x70(%rdi)
> > > > > # Here is where the patching is being done
> > > > >
> > > > > -Nick
> > > > >
> > > > > On Nov 29, 2012, at 11:07 AM, Alexander Potapenko wrote:
> > > > >>> On Thu, Nov 29, 2012 at 9:55 PM, Jack Howarth <
> > > > howarth at bromo.med.uc.edu>
> > > > >>> wrote:
> > > > >>>>
> > > > >>>> Nick,
> > > > >>>> Can you take a quick look at the asan_eh_bug.tar.bz testcase
> > > > >>>> I uploaded into the newly opened radr://12777299, "potential
> > > > >>>> pthread/eh bug exposed by libsanitizer". The FSF gcc developers
> > > > >>>> have ported llvm.org's asan code into FSF gcc (and are keeping
> > > > >>>> it synced to the upstream llvm.org code). I have been helping
> > > > >>>> with the darwin build and testing -fsanitize=address against the
> > > > >>>> complete FSF gcc testsuite. This seems to have exposed a potential
> > > > >>>> bug in pthread or eh on darwin under libasan. Hundreds of test
> > cases
> > > > >>>> in the g++ and libstdc++ testsuites fail under -fsanitize=address
> > > > >>>> in the following manner...
> > > > >>>>
> > > > >>>> ASAN:SIGSEGV
> > > > >>>> =================================================================
> > > > >>>> ==2738== ERROR: AddressSanitizer: SEGV on unknown address
> > > > 0x0000ffd27000
> > > > >>>> (pc 0x0000ffd27000 sp 0x7fff55e40828 bp 0x7fff55e408f0 T0)
> > > > >>>> AddressSanitizer can not provide additional info.
> > > > >>>> #0 0xffd26fff
> > > > (/Users/howarth/asan_eh_bug/./cond1_asan.exe+0xf5f67fff)
> > > > >>>> #1 0x7fff8bd827e0 (/usr/lib/system/libdyld.dylib+0x27e0)
> > > > >>>> #2 0x0
> > > > >>>> Stats: 0M malloced (0M for red zones) by 3 calls
> > > > >>>> Stats: 0M realloced by 0 calls
> > > > >>>> Stats: 0M freed by 0 calls
> > > > >>>> Stats: 0M really freed by 0 calls
> > > > >>>> Stats: 1M (384 full pages) mmaped in 3 calls
> > > > >>>> mmaps by size class: 7:4095; 8:2047; 9:1023;
> > > > >>>> mallocs by size class: 7:1; 8:1; 9:1;
> > > > >>>> frees by size class:
> > > > >>>> rfrees by size class:
> > > > >>>> Stats: malloc large: 0 small slow: 3
> > > > >>>> ==2738== ABORTING
> > > > >>>>
> > > > >>>> The failure of...
> > > > >>>>
> > > > >>>> FAIL: g++.dg/eh/cond1.C -std=c++98 execution test
> > > > >>>>
> > > > >>>> was used as the test case for the radar report and compiled
> > with...
> > > > >>>>
> > > > >>>> g++-fsf-4.8 -static-libasan -fsanitize=address -std=c++98 cond1.C
> > -g
> > > > -O0
> > > > >>>> -o cond1_asan.exe
> > > > >>>>
> > > > >>>> to produce the above failure. When compiled without libasan as...
> > > > >>>>
> > > > >>>> g++-fsf-4.8 -std=c++98 cond1.C -g -O0 -o cond1_no_asan.exe
> > > > >>>>
> > > > >>>> the resulting executable runs fine. Debugging this in gdb seems to
> > > > show
> > > > >>>> that the failure
> > > > >>>> is occuring in the final call to dyld_stub_pthread_once (). The
> > same
> > > > test
> > > > >>>> case
> > > > >>>> compiles fine with -fsanitize=address under llvm 3.2 clang++ and
> > > > produces
> > > > >>>> no runtime errors
> > > > >>>> but the code execution path is very different in that case
> > (because
> > > > of the
> > > > >>>> different
> > > > >>>> libstdc++).
> > > > >>>> Can you take a quick peek at this and determine if this is a
> > darwin
> > > > >>>> pthread or unwinder
> > > > >>>> bug or an issue with libasan that FSF gcc's compiler is exposing?
> > > > Thanks
> > > > >>>> in advance for
> > > > >>>> any help on this.
> > > > >>>> Jack
> > > > >>>> _______________________________________________
> > > > >>>> LLVM Developers mailing list
> > > > >>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> > > > >>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> > > > >>>
> > > > >>>
> > > > >>
> > > > >>
> > > > >>
> > > > >> --
> > > > >> Alexander Potapenko
> > > > >> Software Engineer
> > > > >> Google Moscow
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Alexander Potapenko
> > > > Software Engineer
> > > > Google Moscow
> > > >
> >
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